It's not invoked anywhere by default.
Jump threading over loop headers was never allowed. You can try it and see what happens, but I'm not sure if it would be a good idea to enable it for all target.
I'm testing with a similar patch and I used this check. Wasn't JT over loop headers never allowed because it would turn the loop into irreducible loop, if that is the case this shouldn't be a concern for LateJumpThreading? However, I admit there is no difference in spec2017/perlbench with this.